LightSPEED Technologies' 25XL Active Noise Reduction Headset

When LightSPEED Technologies shattered the ANR headset price barrier in mid-1997, the company's model 20K — priced just over $400 — garnered rave reviews from AVweb and Aviation Consumer, and quickly became the fastest-selling aviation ANR headset ever. A year later, at EAA AirVenture 1998, the company announced a new top-of-the-line $600 model 25K, but engineering and production snags delayed first deliveries for nearly a year. Now renamed the 25XL, LightSPEED's new high-end headset is now in production, and the company is offering a unique trade-in deal for current 20K owners. Is the 25XL worth the extra dough? After flying with one for several weeks, AVweb's Mike Busch offers his detailed critique of the 25XL, and compares it with its lower-priced sibling.

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About the Author ...

Mike Busch is editor-in-chief of
AVweb, a member of the technical staff at Cessna Pilots Association, and in a
prior lifetime was a contributing editor for The Aviation Consumer and IFR
Magazine. A 6,000-hour commercial pilot and CFI with airplane, instrument and
multiengine ratings, Mike has been flying for 36 years and an aircraft owner
for 33. For the past 14 of those years, he's owned and flown a Cessna T310R
turbocharged twin, which he maintains himself. In his never-ending quest to
become a true renaissance man of aviation, Mike's on the verge of earning his
A&P mechanic certificate. Mike and his wife Jan reside on the central
coast of California in a semi-rural area where he can't get DSL or cable
TV.

I was really excited when I first discovered
the LightSPEED 20K headset in June, 1997. After decades of flying with green
headcrushers from David Clark, I was definitely looking for something that
offered more quiet and comfort. I'd flown a few trips with a borrowed Bose
active noise reduction (ANR) headset and it certainly was impressive, but as a
matter of principle I was defiantly unwilling to spend the $1,000 that Bose was
asking. Sorry, folks, that was simply too much — waaay too much — for me to
plunk down for any headset!

The LightSPEED 20K promised similar quiet and comfort for a shade over $400,
which was well under half the price of a Bose and only about $100 more than DC's
top-of-the-line H10-80 passive that I'd been using for years. A test flight
proved to me conclusively that the 20K lived up to its promises. In fact, I
actually found the LightSPEED to be more comfortable than the Bose, and
very nearly as quiet. I was hooked, bought a second 20K for the copilot position
of my Cessna 310, and have been flying with the LightSPEED 20K almost
exclusively for the past two years.

LightSPEED 20K

In July 1997, I wrote a
glowing review of the 20K for AVweb. A few months later, a similarly
effusive review appeared in The Aviation Consumer, and word spread
through online aviation forums and newsgroups. Soon, pilots started ordering
20Ks in droves. LightSPEED was taken by surprised by the demand, and for awhile
pilots who wanted a 20K found themselves waiting a month or more for delivery.
But LightSPEED ultimately ramped up production to meet the demand, and the 20K
has been the industry's best-selling ANR headset ever since.

Since then, I've become totally addicted to my 20Ks. Like most first-time ANR
users, I was worried whether the active cancellation would keep me from hearing
sounds that I really needed to hear — gear, stall and autopilot-disconnect
warnings, clattering valve lifters, that sort of thing. I quickly found out that
I could actually hear these sounds a lot better than before with the
low-frequency prop and exhaust noise actively cancelled out.

Not long after I switched from David Clark H10-80 (DC's quietest passive) to
LightSPEED 20K (ANR), I started hearing a funny "gravelly" sound that I couldn't
identify, mostly during taxi, takeoff, and rollout. Soon, I realized that the
noise stopped when I lifted the nosewheel on takeoff, and reappeared when I
lowered the nosewheel after landing. I disassembled the nosewheel, used solvent
to remove all the grease from the wheel bearings, and discovered a frozen roller
in one of the two Timken roller bearings! I bought a new bearing, regreased both
bearings, and reassembled the nosewheel. On my next flight, the "gravelly" sound
was gone ... and I was irretrievably hooked on ANR!

A Hard Act to Follow

The following year, spurred by LightSPEED's obvious success with the
20K, a number of other headset makers entered the fray by introducing new
low-cost ANR headsets in the $400 range. This included firms who were already
selling higher-priced ANRs (e.g., Telex and David Clark) and others who were
entering the ANR arena for the first time (e.g., Pilot Avionics and FlightCom).
Most of these new entrants offered credible noise-reduction specifications in
the 20-ish decibel range, and some included novel features (like Pilot's
relocation of the batteries into the headset itself). I tried some of these, but
I was hard pressed to find anything that felt as comfortable on my head as the
LightSPEED. (Keep in mind, however, that comfort is a highly subjective matter
— you really owe it to yourself to try as many different makes and models as
you can before you make a choice.)

Meantime, I started hearing rumors that both Bose and LightSPEED would be
introducing new models at EAA AirVenture 1998. As the story went, the new
LightSPEED 25K was to be an evolutionary enhancement to the 20K providing some
additional active noise cancellation, extended battery life, and an
nifty-sounding automatic shutoff feature that would save the batteries from
exhaustion if the user forgot to turn the power off at the end of a flight. (As
someone who was frequently guilty as charged, this latter feature seemed
particularly attractive to me.) The new Bose headset, referred to somewhat
mysteriously as "Model X," was reportedly a radical clean-sheet design featuring
greatly reduced weight and abandonment of Bose's signature breast-implant-like
silicone gel earseals.

Bose Aviation Headset
X

I called both companies to see what I could learn. Bose wasn't talking.
LightSPEED admitted that they were working on a new 25K model, but they weren't
sure whether or not it would be ready for Oshkosh.

At AirVenture 1998, Bose announced the new "Bose Aviation Headset X" and
demoed it, but didn't have any production units to sell at the show.
AVweb's Joe Godfrey — a hardcore Bose afficionado — ordered one of the
$995 X-sets at the show with the promise of "shipping within 30 days." In late
August, he was told to expect "mid-October delivery." Joe finally received his
headset in December, and you can
read his detailed review here on
AVweb.

LightSPEED's announcement of the 25K headset at AirVenture '98 turned out to
be even more premature than Bose's. LightSPEED had no demo units at the show,
and said that shipments of the $599 headset would begin in early October — a
prediction that turned out to be overoptimistic by nearly ten months! As it
turned out, meeting the originally announced active noise cancellation target of
30 dB proved insurmountable (LightSPEED now claims a more realistic 25 to 28 dB
of active cancellation), and getting the automatic shutoff feature to work
reliably turned out to be much tougher than expected (although it now seems to
work quite well indeed). And by the time the headset finally made it into
production in July 1999, its name had changed from "25K" to "25XL" (more on this
later).

LightSPEED also generated a lot of attention at AirVenture when it announced
a unique and unprecedented trade-in program for current owners of LightSPEED 20K
headsets. For $200, owners could trade in their 20K headset for a brand new
25XL. By the time the 25s started shipping in August 1999, well over 1,000
owners were wait-listed to trade their 20Ks. (What the company plans to do with
all those slightly-used 20Ktrade-ins remains unclear.)

Flying the 25XL

LightSPEED had a very limited number of the new 25XLs at AirVenture 1999 and
were guarding them like the crown jewels, but LightSPEED's Alan Schrader was
kind enough to liberate one of the new headset for me to test-fly. My first
opportunity to try it out came immediately after AirVenture, on a 3+30 IFR
flight from Oshkosh to Charlotte, N.C. Since then, I've flown with the 25XL on
several shorter East Coast hops, including a relatively high-workload day-trip
into and out of (ahem) Ronald Reagan Washington National Airport (DCA). During
these flights, I also had my trusty old LightSPEED 20Ks aboard, and was able to
do some "A-B testing" to get a better handle on precisely how the new 25XL
headset differs from its 20K sibling.

Physically, the two headsets are virtually identical. The only real way to
tell them apart visually is by color — the 25XL headband and earcups are dark
charcoal gray, while the 20K is light gray. The 25XL also comes with two
interchangable sets of earseals: standard "soft" seals identical to those on the
20K, and optional "ultra-soft" seals as used on the 15K. I tried both, and found
the ultra-soft seals a tad more comfortable, although using them sacrifices a
bit of noise cancellation and may not provide adequate room to accommodate
large-eared folks. In any case, I think that having the choice is a nice
touch.

Active Cancellation Profiles: 25XL and
20K

The big difference lies in the 25XL's all-new electronics, something that is
immediately apparent when the headsets are first powered up. The 20K ANR cuts in
immediately ("sucking the noise right out of your head"), while the 25XL's seems
to take a second or two to become effective ... a first tip-off of the new
"adaptive" cancellation circuitry. The 25XL also has a slightly different
"sound" compared to the 20K — a bit more emphasis in mid-range frequencies, and
a bit less in highs and lows. Also, the 25XL has more receive gain than previous
LightSPEED headsets in order to improve compatibility with non-LightSPEEED
headsets when several different brands are being intermixed in a single cabin
intercom system.

During cruise flight, I tried repeatedly switching back and forth between the
20K and the 25XL to determine how their noise canceling qualities differed. The
25XL is definitely quieter, but I found the difference in noise cancellation
more subtle than I expected, given the rather large 3 to 4 dB difference in the
factory specifications. (The 20K spec says 22-24 dB of active cancellation,
while the 25XL spec says 25-28 dB.)

A more obvious difference in my "A-B testing" was in microphone equalization.
Again, the 25XL seemed to emphasize the mid-range frequencies and tone down the
highs and lows, compared to my 20K. I found this to be a noticeable improvement,
both in better speech intelligibility and in reduced transmission of cabin "air
noise." One of my pet peeves with the 20K has long been that its mic picks up
too much air noise, to the point of breaking intercom squelch during high-IAS
descents. I found the 25XL was much improved in this regard.

However, in discussing this observation with LightSPEED, I was told that the
factory modified the microphone preamp equalization in 20K headsets manufactured
from about January 1998 on, and my 20Ks are older than that. So it's quite
possible that improvement in microphone response that I noted in the 25XL would
also be found in late-model 20Ks. At this point, I can't be sure.

LightSPEED claims considerably better battery life in the new
25XL: more than 50 hours from a pair of AA-size alkalines, compared to 30 hours
for the 15K and 20K. To be honest, I simply haven't been able to get enough
flight time yet with the 25XL to verify this, but I have no reason to doubt it
because LightSPEEDs have always offered exceptionally long battery life.

I was able to verify the 25XL's auto-shutoff feature, however, and
found that it works remarkably well. Even in a noisy cockpit in flight, I found
that if I removed the 25XL from my head and set it on the glareshield or seat
cushion, the ANR would automatically turn itself off after roughly three
minutes. (To reactivate the ANR after an auto-shutoff, you cycle the power
switch off and back on.) My experience over the past two years has been that
running down batteries by inadvertently forgetting to turn off the power is a
big problem — even if I remember, my copilot might not. Consequently, I'd
expect that the 25XL's auto-shutoff feature is likely to be a big battery
saver.

That goes at least double for folks who carry their headsets with them rather
than leaving them in the airplane the way I do. I've heard a fair number of
gripes from folks who say that it's awfully easy to bump the power switch
accidentally while the 20K is being carried around, resulting in a nasty
surprise and a scramble to find fresh batteries at the start of the next flight.
That should be pretty much a think of the past with the 25XL.

One other 25XL feature worth mentioning is its improved immunity to RFI. The
20K had some problems in this area — its ANR would not work with an ICOM IC-A22
handheld radio, for example, and some problems were reported in Bonanzas and
Barons equipped with comm antennas immediately above the pilot's head.
LightSPEED says that the 25XL does not suffer these problems. (I have not had an
opportunity to verify this independently.)

I can tell you, however, that LightSPEED has not completely eradicated the
proclivity of their headsets to "chirp" slightly when in close proximity to an
ATC radar antenna. The 20K does this, and during my flight to and from DCA, I
found that the 25XL does, too. The muffled chirps are not loud enough to be
especially annoying or distracting, but they certainly can be puzzling until you
realize what's causing them. (This was a much more serious problem in early 20Ks
until LightSPEED came out with a fix in late 1997.)

Tech Talk: How It Works

It's not at all surprising that LightSPEED had a tough time squeezing an
additional 3 or 4 dB of active noise cancellation out of the 25XL, because doing
so is no simple task. It's not just a matter of cranking up the gain on the ANR
circuitry, because doing so will invariably cause the headset to go unstable and
force it into oscillation — very much like what happens when someone turns up
the mic gain on the public address system in an auditorium ... ouch!
Traditionally, engineers have experimentally increased ANR gain to the verge of
instability, then backed it down by a "safety margin" to account for various
operational factors that might trigger oscillation — such as receiving an ATC
transmission, the wearer clenching his teeth, or having an imperfect seal around
the temples of the pilot's sunglasses.

LightSPEED came up with a different and clever approach for the 25XL: add
logic to the electronics that allow the headset to continually readjust its own
ANR gain to be as high as possible without actually going into oscillation. When
some external factor threatens to push the headset into instability, the 25XL
circuitry reacts by automatically reducing the ANR gain to prevent oscillation.
When the factor goes away, the ANR gain is gradually increased again. The result
is a headset that constantly operates as the maximum possible level of active
cancellation at any given moment.

If this sounds tricky, it is. LightSPEED isn't saying much about exactly how
it acomplishes this automatic ANR gain control, and has applied for a patent to
protect its technology. But you can actually hear the circuitry at work if you
know what to listen for. For example, if you lift an earseal from your head in
flight (say, to don an oxygen cannula), you can hear a brief, transient "growl"
as the ANR starts to become unstable, but the oscillation is nipped in the bud
almost immediately as the headset compensates by turning down its ANR gain. When
you put the earseal back into place, you can hear the noise cancellation
increase as the headset slowly restores the ANR gain to its previous value.

The 25XL's auto-shutoff feature is actually a byproduct of this automatic ANR
gain control. If you remove the headset from your head, you create a profoundly
unstable acoustic condition because the earcup cavity is no longer closed. Some
ANR headsets actually start to squeal audibly when removed from the head with
the ANR turned on (I've had this happen with some Telex ANR models, for
example). The 25XL doesn't oscillate in this situation — at least for any more
than a split second — because its automatic logic cranks the ANR gain way down.
At the same time, it says to itself, "this acoustic condition is so unstable
that the headset must be off the wearer's head." If this condition persists
continuously for two to three minutes, the ANR module powers itself down to save
the batteries. LightSPEED has applied for a patent on its auto-shutoff
technique, too.

What's in a Name?

Naturally, I was curious to know why LightSPEED decided to call its latest
headset model 25XL instead of 25K. After talking to the company, I must confess
that I'm still not quite sure. LightSPEED says only that the 25XL is the first
of what is expected to be a new "XL" product line, but it's not at all clear
what additional members of the XL family might be coming down the pike.

One could certainly speculate, for example, that the existing 15K and 20K
might someday be superseded by new 15XL and 20XL models. It would be a fair
guess that such models might share the 25XL's increased battery life (maybe "XL"
stands for "extra life"?), higher receive gain, and improved resistance to RFI.
But let me be quite clear — these are just wild, irresponsible guesses on my
part. LightSPEED's not talking.

What to Do, What to Do?

Okay, okay, so the new LightSPEED 25XL is a
thoroughly delightful headset chock full of the very latest in bleeding-edge
technology ... but is it worth $140 more than the 20K ($599 vs. $439, list)? Or $200 more, if you're a current 20K owners looking to trade up?

That's a tough question.

The 25XL is definitely an improvement over the 20K. It's quieter, but subtly
so — enough to notice, but not enough to make you cry "Wow!" The equalization
is a little better in terms of fidelity and intelligibility. Battery longevity
is greatly improved, particularly if you consider the unit's auto-shutoff
feature that is bound to save a lot of batteries and "expletives deleted."

On the other hand, if you're expecting the extra $140 or $200 to buy the same
magnitude of improvement that you got by going from a $300-ish passive headset
to a $400-ish ANR, you're going to be sorely disappointed. This is by no means a
criticism of the 25XL, so much as acknowledgement that the 20K is already a
phenomenally good headset and mighty hard to improve upon.

Let's face it: The 20K offers every bit as much comfort as the 25XL
(physically, they're identical twins), every bit as much passive noise reduction
(same earcups and earseals), and is no slouch in the active cancellation
department, either. The 25XL's auto-shutoff is a great feature, but then again
you can buy a whole lot of AA batteries for $140!

So, bottom line, would I spend $599 to buy the new 25XL? Yes, I might ... but
the 20K would be a mighty tempting alternative (especially at a "street price"
around $400 that you can sometimes get from discounters like Avionics West when they get
temporarily overstocked and put the units on sale).

Will I shell out $200 to trade my 20K in for a new 25XL? The verdict isn't in
on that one yet, but I'm certainly not in a big hurry to do so. Nothing against
the 25XL, mind you — it's quite a marvel of acoustic and electronic
engineering. But I'm still mighty happy with my 20Ks, and I fully expect to be
flying with them for years to come.

But then again, I own three automobiles, and the newest of those is a 1985
model. Not to mention that I'm typing this article on an old notebook computer
with a slow-poke 166 MHz CPU. So you may want to get a second opinion.

Better yet, find a way to test-fly the headsets for yourself. As I mentioned
earlier, choosing a headset is an extremely subjective matter, and you should
never make a purchase decision solely on the basis of someone else's evaluation.
Even mine. Especially mine!

Where to Buy

LightSPEED has a web site where you can review
the features and specifications of LightSPEED ANR models, read answers to
frequently-asked questions, learn a great deal about the theory and design of
ANR headsets in general (and LightSPEED's in particular), and order the headsets online.

LightSPEED ANR headsets are also available from a number of
dealers, some of whom offer the headsets at small discounts from list. (There's
not a lot of dealer margin on these units, so don't expect big discounts.) One
of LightSPEED's "preferred dealers" is Avionics West, Inc., who
maintains an online site and accepts online orders for all LightSPEED headset
models (as well as a number of other brands).